Yamagata Masakage (山県 昌景, 1524 – June 29, 1575) was one of the 24 generals of the Takeda clan. He was famous for his red armour and skill in battlefield, and was a personal friend of Takeda Shingen. He was the younger brother of Obu Toramasa who was also a retainer of Shingen leading the famous "red fire unit" (derived from Shingen's slogan Fūrinkazan). After his brother committed Seppuku as a cover for Takeda Yoshinobu's failed rebellion, Masakage took the red fire unit title and outfitted his cavalry in bright red armor. It was said that his cavalry would always charge first in battle; sowing confusion and panic in the enemy ranks.
Yamagata was a fierce warrior who fought in many battles and was given a fief in Shinano. He was present at the Battle of Mimasetoge in 1569 and captured Yoshida Castle, a Tokugawa possession, during the Mikatagahara Campaign (1572–73) and was present for the following Battle of Mikatagahara. His last campaign was in the ill fated Battle of Nagashino in 1575 where he was shot down on horse while charging together with his famous red fire unit. All of them died together with him.
Yamagata tried to persuade Takeda Katsuyori to call off twice at the attack of Nagashino, as he knew there was a trap waiting for them, however Katsuyori didn't listen.
Ii Naomasa from the Tokugawa clan was inspired by Yamagata's red colour, he made tribute to him by naming his army the "Red Devil Brigade."
According to legend, Shingen called out to Yamagata from his deathbed in 1573 and ordered him to plant his banners at the Seta Bridge, the traditional eastern gateway to Kyôto.
He appears as one of the main characters in Akira Kurosawa's epic Kagemusha. In the movie he appears to be openly critical (albeit as a friend) towards the "real" Shingen.
Yamagata's role at Nagashino is often downplayed in video games based on the event (Samurai Warriors, Devil Kings and the like). He is usually replaced by Sanada Yukimura, although Yukimura does wear Yamagata's signature red armor.